The present invention relates to a method for preventing leaching of contaminants from the surface of a solid or, in particular, to a method for preventing contamination of a material in contact with a solid such as a glass, ceramic, metal and the like by the ingredients leached out of the surface of the solid.
In various kinds of fine technologies such as the manufacture and processing of semiconductors or semiconductor devices, preparation and storage of medicines and microanalytical procedures, it is of utmost importance to avoid contamination of the materials or chemicals under handling by trace amounts of impurities, especially, such as alkali metals originating in the solid surface with which the material or the chemical in question is in contact. For example, contamination with an alkali metal element is unavoidable when the material or chemical is contained in a vessel or handled with a tool made of a glass because containers for photoresist materials, glass bottles for reagents and medicines, ampules, beakers and flasks made of glass cannot be free from the problem of exudation or leaching out of the ingredients of the glass such as alkali metals so that the chemicals contained in such vessels are always subject to contamination with an alkali metal. In the manufacuture of semiconductors, in particular, contamination with a trace amount of alkali metal ions may sometimes be very detrimental for the performance of the semiconductor produced under the contamination.
Most of the glass vessels or tools used for handling chemicals are made of a glass belonging to the class of so-called soda glass and are rather disadvantageous from the standpoint of contamination by the ingredients leached out of the surface even when they are used after the most careful cleaning treatment by dipping in a chromic acid mixture or in a strong alkali solution for several days to have the surfaces freed from the contaminants.
When the contamination from the vessels or tools must be minimized to an extremely low extent, several kinds of materials with little leaching out of the ingredients, such as borosilicate glass, high-silicate glass and fused quartz glass, are employed or, alternatively, a protective film of a fluorocarbon polymer is provided on the surface of the vessel or tool. These vessels or tools are, however, very expensive and they are not always suitable for industrial uses. Accordingly, it has long been desired to develop a simple and effective means with less expensive materials by which the leaching out of contaminants can be prevented regardless of the materials of the substrate solid surfaces.